Coordination polymers and hydrogen-bonded assemblies of 2,2′-[2,5-bis(carboxymethoxy)-1,4-phenylene]diacetic acid with ammonium, lanthanum and zinc cations

Abstract

We report the synthesis of the 2,2'-[2,5-bis(carboxymethoxy)-1,4-phenylene]diacetic acid (TALH(4)) ligand and the structures of its adducts with ammonium, namely diammonium 2,2'-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetate, 2NH(4)(+).C(14)H(12)O(10)(2-), (I), lanthanum, namely poly[[aquabis[mu(4)-2,2'-(2-carboxylatomethyl-5-carboxymethyl-1,4-phenylenedioxy)diacetato]dilanthanum(III)] monohydrate], {[La(2)(C(14)H(11)O(10))(2)(H(2)O)].H(2)O}(n), (II), and zinc cations, namely poly[[{mu(4)-2,2'-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetato}zinc(II)] trihydrate], {[Zn(C(14)H(12)O(10))].3H(2)O}(n), (III), and poly[[diaqua(mu(2)-4,4'-bipyridyl){mu(4)-2,2'-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetato}dizinc(II)] dihydrate], {[Zn(2)(C(14)H(10)O(10))(C(10)H(8)N(2))(H(2)O)(2)].2H(2)O}(n), (IV), the formation of all four being associated with deprotonation of TALH(4). Adduct (I) is a diammonium salt of TALH(2)(2-), with the ions located on centres of crystallographic inversion. Its crystal structure reveals a three-dimensional hydrogen-bonded assembly of the component species. Reaction of TALH(4) with lanthanum trinitrate hexahydrate yielded a two-dimensional double-layer coordination polymer, (II), in which the La(III) cations are nine-coordinate. With zinc dinitrate hexahydrate, TALH(4) forms 1:1 two-dimensional coordination polymers, in which every Zn(II) cation is linked to four neighbouring TALH(2)(2-) anions and each unit of the organic ligand is coordinated to four different tetrahedral Zn(II) cation connectors. The crystal structure of this compound accommodates molecules of disordered water at the interface between adjacent polymeric layers to give (III), and it has been determined with low precision. Another polymer assembly, (IV), was obtained when zinc dinitrate hexahydrate was reacted with TALH(4) in the presence of an additional 4,4'-bipyridyl ligand. In the crystal structure of (IV), the bipyridyl and TAL(4-) entities are located on two different inversion centres. The ternary coordination polymers form layered arrays with corrugated surfaces, with the Zn(II) cation connectors revealing a tetrahedral coordination environment. The two-dimensional polymers in (II)-(IV) are interconnected with each other by hydrogen bonds involving the metal-coordinated and noncoordinated molecules of water. TALH(4) is doubly deprotonated, TALH(2)(2-), in (I) and (III), triply deprotonated, viz. TALH(3-), in (II), and quadruply deprotonated, viz. TAL(4-), in (IV). This report provides the first structural characterization of TALH(4) (in deprotonated form) and its various supramolecular adducts. It also confirms the potential utility of this tetraacid ligand in the formulation of coordination polymers with metal cations.